Eur. Phys. J. E 8, 209-216 (2002)
DOI: 10.1140/epje/i2001-10072-0
Enthalpy recovery of a glass-forming liquid constrained in a nanoporous matrix: Negative pressure effects
S.L. Simon1, J.-Y. Park2 and G.B. McKenna11 Department of Chemical Engineering, Texas Tech University, Lubbock, TX 79409-3121, USA
2 E-Polymer Lab, Samsung Advanced Institute of Technology, Daejon, Korea 305-380
sindee.simon@coe.ttu.edu
joonypark@sait.samsung.co.kr
greg.mckenna@coe.ttu.edu
(Received 3 September 2001)
Abstract
The
of organic liquids confined to nanoporous matrices and that of
thin polymer films can decrease dramatically from the bulk value. One
possible explanation for this phenomenon is the development of hydrostatic
tension during vitrification under confinement that results in a concomitant
increase in the free volume. Here we present experimental evidence and
modeling results for ortho-terphenyl (o-TP) confined in pores as small as
11.6 nm that indicate that, although there is an important hydrostatic
tension in the liquid in the pores, it does not develop until near the
reduced
of the constrained material -well below the bulk
. Enthalpy recovery for the o-TP in the nanopores exhibits
accelerated physical aging relative to the bulk, as well as a leveling off
of the fictive temperature at equilibrium values greater than the aging
temperature. An adaptation of the structural recovery model that
incorporates vitrification under isochoric conditions is able to provide a
quantitative explanation for the apparently anomalous aging observed in
nanopore confined liquids and in thin polymeric films. The results strongly
support the existence of an intrinsic size effect as the cause of the
reduced
.
61.20.-p - Structure of liquids.
61.43.Fs - Glasses.
64.70.Pf - Glass transitions.
65.60.+a - Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc..
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2002
